I believe that KL flights are reserved for KL crew, and the same thing goes for Northwest. However, I believe that KL hires pilots of American nationality (it would probably help to learn Dutch, even though most Dutch people know English.

Correct me if I'm wrong, but I think KL only operates one type of aircraft that NW operates (747-400), so the question of NW pilots flying KL planes and vice versa would almost be a moot point.

In the dark days of pilot furloughs at NWA ( 1992-1993) a group of NWA pilots were TDY assigned to fly for KLM as second officers on the 747. They were based in AMS and flew with the Dutch crews. There are'nt any NWA pilots at KLM now or vice versa. I know at least 2 pilots who are from Canada who fly for KLM. Last year KLM did try to place some of their pilots at NWA however that proposal did not come to fruition because of the labor laws that prevent this in the USA.